1. Field of the Invention
The present application concerns improved negative working photoresist compositions containing
a) a polyimide primer (i.e. precursor) containing recurring structural units of formula (I) ##STR1## in which
A.sub.1 stands for an oxygen atom or an NH group,
R.sub.1 represents the same or different residues with at least one photopolymerizable olefin double bond, X! indicates the residue of the cyclic dianhydride of the same or different tetracarboxylic acids remaining after removal of the anhydride groups, and Y indicates the residue of the same or different diamines remaining after removal of the amino groups, as well as
b) a photoinitiator for polymerizing olefin double bonds.
2. Brief Description of Relevant Art
Photoresists of the initially known type have already been known for a long time and are described, for example, in DE-A-2,308,830; DE-A 2,437,348; EP-A-0 119,162, or EP-A-0 624,826. The named photoresist compositions are crosslinked upon action of irradiation of suitable wavelength by means of the photopolymerizable olefin double bonds in the polyimide primer and thus represent negative resists. The named resists have a very high sensitivity and show only a small amount of dark material removed during development. Further, they have the advantage that a coating that is prepared with their help can be transformed into a polyimide coating after exposure and developing by firing, whereby the coating is particularly heat resistant. However, a disadvantage is that such negative resists must be treated beforehand with developers that consist almost completely of organic solvents, which, of course, is not desirable due to the expenditures associated therewith for environmentally compatible disposal as well as for reasons of inflammability.
On the other hand, aqueous-alkaline developable positively operating photoresists based on polyimide primers, including those of above formula (I), are described in WO-A-93/09470. The compositions also contain, as aqueous-alkaline developable photoresists, compounds that decompose under the effect of radiation into components that are soluble in alkali, particularly 1,2-diazoquinone derivatives, as have been used for a long time in commercial positive resists based on novolak resins. In order to improve their developability in aqueous-alkaline media, the named positive photoresist compositions also contain solubility reinforcers, particularly hydroxy compounds, which essentially increase the solubility of the irradiated resist parts in the developer, but the solubility of the unexposed resist parts is only slightly increased or is not increased at all. Particularly preferred solubility reinforcers are organosilanols, such as triphenylsilanol, diphenylsilanediol, and 1,4-bis (hydroxydimethylsilyl)benzene, as well as organosiloxanes with free hydroxyl groups, such as 1,3-bis(4-hydroxybutyl)-tetramethyldisiloxane.
One task of the present invention is to make available a negative working photoresist composition based on polyimide primers or precursors of the above named formula (I), which makes possible, under the usual conditions of practice, the use of developers that comprise aqueous-alkaline media.